<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let num1 = +prompt('请输入第一个数字')
        let ope = prompt('请输入运算符')
        let num2 = +prompt('请输入第二个数字')
        let sum
        switch (ope) {
            case '+':
                sum = num1 + num2
                alert(sum)
                break
            case '-':
                sum = num1 - num2
                alert(sum)
                break
            case '*':
                sum = num1 * num2
                alert(sum)
                break
            case '/':
                sum = num1 / num2
                alert(sum)
                break
            default: alert('输入错误')
                break
        }
    </script>
</body>

</html>